The present invention relates to friction clutches in general, especially to multiple-disc or multiple-plate friction clutches, and more particularly to improvements in friction clutches of the type wherein a diaphragm spring (also called cup spring or belleville washer) is disposed between two axially movable pressure plates so that a first portion thereof engages one of the pressure plates and a second portion thereof (which is located radially inwardly of the first portion) engages the other pressure plate in order to urge the two pressure plates against discrete clutch discs or clutch plates.
Friction clutches of the above outlined character are disclosed, for example, in commonly owned German Offenlegungsschrift No. 2,146,587, in commonly owned U.S. patent application Ser. No. 232,246, filed Feb. 6, 1981 by Paul Maucher, now U.S. Pat. No. 4,429,716, for "Double Friction Clutch", and in German Offenlegungsschrift No. 2,147,035. Such clutches are often used in special types of conveyances, for example, in tractors, implement carriers, building machinery and others. Depending on the intended use and/or design of a multiple-plate friction clutch, the various clutch units (each having a clutch plate and a pressure plate) can be actuated (i.e., engaged and/or disengaged) simultaneously, independently of one another or in a given sequence. Each disengagement involves axial movement of the respective pressure plate away from the associated clutch plate. In double-plate friction clutches wherein one of the pressure plates is moved axially after the other pressure plate, the actuating means normally comprises three levers. On the other hand, a double-plate friction clutch wherein each of the pressure plates can be moved independently of the other pressure plate normally comprises two sets of levers and each such set normally comprises three discrete levers.
The diaphragm spring of a multiple-plate friction clutch constitutes a component part whose design must be selected with utmost care because the spring must stand very pronounced stresses. The diaphragm spring should be capable of transmitting pronounced forces (such forces are applied to the pressure plates to urge the latter against the respective clutch plates which, in turn, bear against torque-transmitting devices in the form of rotary housings, flywheels or the like), and the diaphragm spring should also have a long useful life in spite of frequent and pronounced dynamic stressing. An additional problem which must be solved is that, under certain circumstances, each of the two pressure plates which flank the diaphragm spring must be disengaged from the respective clutch plate at the same time so that the diaphragm spring of such multiple-plate friction clutch must undergo very pronounced deformation which is approximately twice that of a diaphragm spring in a simple friction clutch with one pressure plate.
Commonly owned German Offenlegungsschrift No. 3,013,298 discloses a multiple-plate friction clutch with several clutch units wherein a single diaphragm spring is common to the two units, i.e., a single diaphragm spring can displace two axially movable pressure plates. The diaphragm spring comprises a circumferentially complete outer marginal portion and radially inwardly extending prongs alternating with elongated open slots. The prongs act not unlike levers which displace the actual diaphragm spring, namely, the aforementioned outer marginal portion, in response to the application of a pressure or pull upon their inner end portions or tips. The prongs ensure uniform stressing of the outer marginal portion when the latter is tilted to change the extent of its conicity.